Systems and methods for calibrating an optical distance sensor

ABSTRACT

A calibration system is provided including an aperture layer, a lens layer, an optical filter, a pixel layer and a regulator. The aperture layer defines a calibration aperture. The lens layer includes a calibration lens substantially axially aligned with the calibration aperture. The optical filter is adjacent the lens layer opposite the aperture layer. The pixel layer is adjacent the optical filter opposite the lens layer and includes a calibration pixel substantially axially aligned with the calibration lens. The calibration pixel detects light power of an illumination source that outputs a band of wavelengths of light as a function of a parameter. The regulator modifies the parameter of the illumination source based on a light power detected by the calibration pixel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/419,053 filed Jan. 30, 2017, which claims the benefit of U.S.Provisional Patent Application No. 62/289,004 filed Jan. 29, 2016, thedisclosures of each of which are hereby incorporated by reference intheir entirety.

TECHNICAL FIELD

This disclosure relates generally to the field of optical sensors andmore specifically to a new and useful system and method for calibratingan optical distance sensor in the field of optical sensors.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a system according to a firstembodiment herein;

FIG. 2A is a schematic representation according to a second embodimentherein;

FIGS. 2B, 2C, and 2D are graphical representations of the secondembodiment herein;

FIGS. 3A and 3B are schematic representations according to a thirdembodiment herein;

FIG. 4 is a schematic representation according to a fourth embodimentherein.

DESCRIPTION OF THE EMBODIMENTS

The following description of embodiments of the invention is notintended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.Variations, configurations, implementations, example implementations,and examples described herein are optional and are not exclusive to thevariations, configurations, implementations, example implementations,and examples they describe. The invention described herein can includeany and all permutations of these variations, configurations,implementations, example implementations, and examples.

1. System

As shown in FIG. 1, in one embodiment, a calibration system 100 (e.g.,for calibrating an optical distance sensor) includes: a bulktransmitting optic 101 and a bulk receiving optic 102. The system 100may also include an illumination source 103 offset behind the bulktransmitting optic and configured to output a wavelength of light as afunction of temperature; an aperture layer 104 arranged behind the bulkreceiving optic and defining a sense aperture 120 and a calibrationaperture 125; an optical bypass 105 extending from the illuminationsource behind the bulk transmitting optic to the calibration aperture; alens layer 106 adjacent the aperture layer opposite the bulk receivingoptic, comprising a sense lens 107 substantially axially aligned withthe sense aperture, and comprising a calibration lens 108 substantiallyaxially aligned with the calibration aperture; an optical filter 109adjacent the lens layer opposite the aperture layer; a pixel layer 110adjacent the optical filter opposite the lens layer, comprising a sensepixel 111 substantially axially aligned with the sense lens, andcomprising a calibration pixel 112 substantially axially aligned withthe calibration lens; and a temperature regulator 113 coupled to theillumination source and configured to modify a temperature of theillumination source based on a light power detected by the calibrationpixel. In the embodiment of FIG. 1, system 100 may also include diffuser170 configured to guide light onto the photodetectors. In oneembodiment, the diffuser may be included in an optional converging lenslayer arranged so as to converge light onto the photodetectors. Theconverging lens layer may be arranged between the optical filter and thephotodetector. The converging lens layer may also comprise a micro-lens,a plurality of micro-lenses, a diffuser, or any other element capable ofguiding light onto the photodetectors. In addition, in the embodiment ofFIG. 1, system 100 may be housed in a housing 135. Although variouslayers have been described in the foregoing embodiment as being adjacentto another layer, it will be appreciated that fewer or additional layersmay be included. For example, it will be understood that additionalaperture layers may be included between any two layers.

As shown in FIG. 3A, system 300 is an embodiment of a variation of thesystem 100, where the system 300 may include: a bulk transmitting optic301; a bulk receiving optic 302; an illumination source offset behindthe bulk transmitting optic and configured to output a wavelength oflight as a function of temperature; an aperture layer 304 defining afirst calibration aperture and a second calibration aperture; an opticalbypass 305 extending from the illumination source behind the bulktransmitting optic to the first calibration aperture and the secondcalibration aperture; a lens layer 306 adjacent the aperture layeropposite the optical bypass, comprising a first calibration lenssubstantially axially aligned with the first calibration aperture, andcomprising a second calibration lens axially offset from the secondcalibration aperture; an optical filter 309 adjacent the lens layeropposite the aperture layer; a pixel layer adjacent the optical filteropposite the lens layer, comprising a first calibration pixelsubstantially axially aligned with the first calibration lens, andcomprising a second calibration pixel aligned with a ray extendingthrough the second aperture and the second calibration lens; and atemperature regulator 313 coupled to the illumination source andconfigured to modify a temperature of the illumination source based on alight power detected by the first calibration pixel and the secondcalibration pixel. System 300 also may include a second illuminationsource 350, in addition to illumination source 303.

2. Applications

In one embodiment, the system 100 functions as an image sensor that,when rotated about an axis parallel to a column of sense apertures,collects three-dimensional distance data of a volume occupied by thesystem 100. Similarly, the system 100 can function as a static imagesensor that collects two- or three-dimensional distance data of a spaceor volume in the field of view of the system 100. Generally, the system100 can scan a volume to collect three-dimensional distance data thatcan then be reconstructed into a virtual three-dimensionalrepresentation of the volume, such as based on recorded times betweentransmission of an illuminating beam from the illumination source anddetection of photons—likely originating from the illuminationsource—incident on the sense pixel, based on phase-based measurementtechniques, or based on another distance measurement technique.

In one embodiment, the system 100 includes an illumination source, acalibration circuit 130, and a sensing circuit. The sensing circuitincludes a sense aperture, a sense lens, and an optical filter thatcooperate to pass only a relatively narrow band of wavelengths of light(e.g., a single target wavelength +/−0.25 nanometers) to a correspondingsense pixel. Because the sensing circuit is configured to detect lightin only a relatively narrow wavelength band, the system 100 can tune theillumination source to output light within this relatively narrowwavelength band. The illumination source can output a narrow band ofwavelengths of light in a distribution pattern centered at a wavelength.The center frequency of the light source can be varied by changing thetemperature of the illumination source (the preferred mode), thoughalternately it can be done by changing the duty cycle of the source, byusing piezo effect, or any other means available. The calibrationcircuit can actively control the source temperature by aregulator—thermally coupled to the illumination source—in order togovern the center wavelength of light output by the illumination source.In particular, the calibration circuit can match the center wavelengthof light output by the illumination source to the center wavelengthpassed and detected by the sensing circuit in order to substantiallymaximize the energy efficiency of any receiver system such as the system100 (i.e., a ratio of light read by the sensing circuit to light outputby the illumination source).

The optical filter in the sensing circuit may pass and reject light as afunction of incident angle, and manufacturing defects may yield alateral and/or longitudinal offset between the aperture layer and thelens layer such that the sense aperture and the sense lens are notaxially aligned and such that light output from the sense lens reachesthe optical filter at an angle other than perpendicular to the opticalfilter. Misalignment between the aperture layer and the lens layerduring manufacture may therefore yield a sensing circuit that passes anddetects a center wavelength of light other than a nominal wavelengththat the optical filter is configured to pass (i.e., a center wavelengththat the optical filter passes for light incident on the optical filterat) 90°, as shown in FIG. 2B. Furthermore, such misalignment betweenaperture layers and lens layers may not be uniform from one unit of thesystem 100 to the next and may vary over time within a single unit ofthe system 100, such as due to ambient temperature and/or pressure.Similarly, illumination sources (e.g., bar diode lasers) may exhibitdifferent output characteristics (e.g., variations in center or primaryoutput wavelength at a particular operating temperature), even within asingle batch of illumination sources, due to manufacturing defects.

Therefore, rather than implement an illumination source-specific centeroutput wavelength versus temperature model and an empirically-determinedtarget center wavelength for the aperture layer and lens layer stack,the system 100 can incorporate a calibration circuit—similar to thesensing circuit—and can actively modify an output of the temperatureregulator based on light detected by the calibration circuit. Inparticular, the calibration circuit: can include a calibration apertureintegrated in the same aperture layer as the sense aperture; can includea calibration lens integrated into the same lens layer as the senselens; can share the optical filter (e.g., an optical filter layer) withthe sensing circuit; and can include a calibration pixel integrated intothe same pixel layer as the sensing circuit. The calibration circuit cantherefore mimic manufacturing defects occurring in the sensing circuitsuch that tuning the illumination source to achieve peak incident lightthrough the calibration circuit similarly tunes the illumination sourceto the sensing circuit. In particular, a unit of the system 100 canactively manipulate the temperature regulator to maintain peak incidentphoton count per unit time at the calibration pixel throughoutoperation, thereby matching the output of the illumination optic to boththe calibration circuit and the sensing circuit and automaticallycompensating for substantially unique stacks of manufacturing defects inthe unit of the system 100 with a closed-loop feedback model common to amass of units of the system 100.

Generally, peak incident photon count recorded by the calibration pixelmay occur when the output wavelength of the illumination source ismatched to the bulk peak-power wavelength of the calibration circuit.The calibration circuit and the sensing circuit share a common opticalfilter, include apertures defined by a common aperture layer, includelenses in a common lens layer, and are subject to common lateral andlongitudinal offsets between apertures and lenses. Therefore, the bulkpeak-power wavelength of the sensing circuit is substantially identicalto the bulk peak-power wavelength of the calibration circuit. In orderto increase (or substantially maximize) efficiency of the system 100during operation, the system 100 can uniquely calibrate the illuminationsource to the sensing circuit by tuning the output wavelength of theillumination source to achieve a peak incident photon count per unittime at the calibration pixel. For example, the illumination source canoutput light at a center wavelength that varies proportionally with thetemperature of the illumination source, and the system 100 can controlthe center output wavelength of the illumination source by activelymanipulating heat flux of the temperature regulator coupled to theillumination source. Throughout operation, the system 100 can implementclosed-loop feedback techniques to actively control the output of thetemperature regulator—and therefore the center output wavelength of theillumination source—based on incident photon counts read from thecalibration pixel such that the illumination source remains tuned to thesensing circuit over time despite changes in internal temperature,ambient temperature, ambient pressure, etc.

As shown in FIG. 2A, in one embodiment, a system 200 can includemultiple calibration circuits. The system 200 may include a bulktransmitting optic 201, a bulk receiving optic 202, an optical filter209, a sense aperture 220, a sense lens 207, a sense pixel 211,illumination sources 203 and 250, and an optical bypass 205. Thesecomponents may be structured similarly to the components described abovein connection with FIG. 1. In this variation, each calibration apertureand calibration lens (e.g., calibration apertures 225 and calibrationlenses 208, or individually as calibration apertures 225-1, 225-2,225-3, 225-4 and calibration lenses 208-1, 208-2, 208-3, 208-4) can beoffset by a unique distance (e.g., distance d₀, d₁, d₂, d₃, etc.) in theset such that the calibration lens outputs light toward the opticalfilter at a unique nominal angle (e.g., angle α₀, α₁, α₂, α₃, etc.) inthe set. For example, the system 100 can include a first calibrationaperture and lens set, a second calibration aperture and lens set, athird calibration aperture and lens set, and a fourth calibrationaperture and lens set assembled at unique offset distances such that thefirst, second, third, and fourth calibration lens output light towardthe optical filter at 0°, 1°, 2°, and 3° to the optical filter,respectively, as shown in FIGS. 2A and 2C. Thus, in one embodiment,calibration apertures can be offset from the calibration lenses. Ofcourse, in other embodiments, any number of calibration circuits (e.g.,set of calibration aperture, lens, pixel) may be included in the system.In this variation, the system 200 can read incident photon counts (ortimes between consecutive incident photons, etc.) from each ofcalibration pixels 212 (individually calibration pixels 212-1, 212-2,212-3, 212-4) during a sampling period, determine if the center outputwavelength of the illumination source is greater than or less than thecenter wavelength read by the calibration circuit (and therefore read bythe sensing circuit) during the sampling period based on this set ofincident photon counts, and then increase or decrease the temperature ofthe illumination source—via the temperature regulator—accordingly toimprove alignment of center wavelengths output by the illuminationsource and read by the calibration circuit.

3. Sensing Circuit

As shown in FIGS. 1 and 4, in some embodiments, the sensing circuit ofthe system 100 (and system 400) may include: a bulk receiving optic(e.g., 102 and 402); an aperture layer arranged behind the bulkreceiving optic and defining a sense aperture and a calibrationaperture; a lens layer (e.g., 107 and 407) adjacent the aperture layeropposite the bulk receiving optic and defining a sense lenssubstantially axially aligned with the sense aperture; an optical filter(e.g., 109 and 409) adjacent the lens layer opposite the aperture layer;and a pixel layer (e.g., 111 and 411) adjacent the optical filteropposite the lens layer and including a sense pixel substantiallyaxially aligned with the sense lens. Generally, the bulk receivingoptic, sense aperture, sense lens, optical filter, and the sense pixelcooperate to collect light (e.g., ambient light and light output by theillumination source), to collimate light, to reject all light outside ofa narrow band of wavelengths including a center output wavelength of theillumination source, and to detect light reaching the sense pixel. Thesystem 100 (e.g., a processor within the system 100) can thus transforman incident photon count, a time between incident photons, an incidentphoton time relative to an illumination beam output time, etc. into aposition of a surface in a field of view of the sensing circuit. Asshown in FIG. 4, similar to system 100, system 400 may also include bulktransmitting optic 401, illumination sources 403 and 450, optical bypass405, regulator 413 and calibration circuit 430. These components may bestructured similarly to those described in connection with system 100 ofFIG. 1. As also shown in FIG. 4, system 400 may include an aperturepitch distance 440.

In one implementation, the bulk receiving optic functions to projectincident light rays from outside the system 100 toward a focal planewithin the system 100. For example, the bulk receiving optic can definea converging lens and can include multiple lenses, such as one or morebi-convex lenses (shown in FIGS. 1 and 4) and/or plano-convex lenses,that cooperate to yield a total bulk focal length at or near the centerwavelength of perpendicular light rays passed by the optical filter(i.e., the nominal operating wavelength of the system 100). The aperturelayer includes a relatively thin opaque structure coincident the focalplane (i.e., offset from the bulk receiving optic behind the bulk focallength) and defining the sense aperture and a stop region around thesense aperture. The stop region of the aperture layer rejects (e.g.,blocks, absorbs, reflects) incident light rays, and the sense aperturepasses incident light rays toward the sense lens. For example, theaperture layer can define a sense aperture of diameter approaching adiffraction-limited diameter to maximize geometrical selectivity of thefield of view of the sensing circuit.

In this implementation, the sense lens is characterized by a sense focallength, is offset from the focal plane by the sense focal length,collimates lights rays passed by the sense aperture, and passescollimated light rays into the optical filter. For example, the senselens can include a converging lens characterized by a ray conesubstantially matched to a ray cone of the bulk receiving optic and canbe offset from the focal plane of the bulk receiving optic by arelatively short sense focal length to preserve the aperture of the bulkreceiving optic and to collimate light passed by the sense aperture. Theoptical filter receives collimated light—in a spectrum ofwavelengths—from the sense lens, passes a relatively narrow band ofwavelengths of light (e.g., the operating wavelength +/−0.25 nanometers)to the sense pixel, and blocks light outside of this narrow wavelengthband. For example, the optical filter can include a narrow opticalbandpass filter.

For example, the illumination source can output light (predominantly) ata nominal wavelength of 900 nm, and the optical filter can define aplanar optical bandpass filter configured to pass light (incident on theoptical filter at an angle of 90°) between 899.95 nm and 900.05 nm andconfigured to block substantially all light (incident on the opticalfilter at an angle of 90°) outside of this band. The sense pixelfunctions to receive light (i.e., “photons”) passed by the opticalfilter, to detect these incident photons, and to output a signalcorresponding to a number or rate of detected photons. For example, thesense pixel can include an array of single-photon avalanche diodedetectors (“SPADs”), and the sense pixel can output a single signal or astream of signals corresponding to the count of photons incident on thepixel within a single sampling period picoseconds, nanoseconds,microseconds, or milliseconds in duration.

In one variation, the system 300 includes multiple sensing circuits 340(or individually 340-1, 340-2, 340-3, and 340-4), including multiplesense aperture, sense lens, and sense pixel sets, as shown in FIGS. 3Aand 3B. For example, the system 300 can include: a column of offsetsense apertures 320 (individually 320-1, 320-2, etc.) arranged behindthe single bulk receiving optic and defining discrete (i.e.,non-overlapping beyond a threshold distance from the system 100) fieldsof view in a field ahead of the bulk receiving optic. In one embodiment,each of sense apertures 320 are respectively aligned with acorresponding sense lens. The system 300 may also include anillumination source that projects discrete illuminating beams at anoperating wavelength into the field of view defined by each senseaperture; a column of sense lenses that collimate light rays passed bycorresponding sense apertures; the optical filter that spans the columnof sense lenses and selectively passes a relatively narrow band ofwavelengths of light; and a set of sense pixels that detect incidentphotons, such as by counting incident photons or recording times betweenconsecutive incident photons. In this example, the system 100 canselectively project illuminating beams into a field ahead of the system100 according to an illumination pattern that substantially matches—insize and geometry across a range of distances from the system 100 —thefields of view of the sense apertures. In particular, the illuminationsource can illuminate substantially only surfaces in the field ahead ofthe system 100 that are within the fields of view of corresponding sensepixels such that minimal power output by the system 100 via theillumination source is wasted by illuminating surfaces in the field forwhich the sense pixels are blind. Therefore, the system 100 can achievea relatively high ratio of output signal (i.e., illuminating beam power)to input signal (i.e., photons passed to an incident on the pixelarray), particularly when the center output wavelength of theillumination source is matched to the center wavelength read by thesensing circuit.

In another variation, the system 100 includes a two-dimensional gridarray of sensing circuits (i.e., sense aperture, sense lens, and sensepixel sets) and is configured to image a volume occupied by the system100 in two dimensions per sampling period. In this variation, the system100 can collect one-dimensional distance data (e.g., counts of incidentphotons within a sampling period and/or times between consecutivephotons incident on sense pixels corresponding to known fields of viewin the field) across a two-dimensional grid of sense pixels, and thesystem 100 can merge these one-dimensional distance data with knownpositions of the fields of view for each sense pixel to reconstruct avirtual three-dimensional representation of the field ahead of thesystem 100. For example, the aperture layer can define a 24-by-24 gridarray of 200-μm-diameter sense apertures offset vertically and laterallyby an aperture pitch distance of 300 μm, and the lens layer can includea 24-by-24 grid array of sense lenses offset vertically and laterally bya lens pitch distance of 300 μm. In this example, the pixel layer caninclude a 24-by-24 grid array of 300-μm-square sense pixels, whereineach sense pixel includes a 3×3 square array of nine 100-μm-squareSPADs.

In one implementation, the bulk receiving optic, the aperture layer, thelens layer, the optical filter, and the diffuser are fabricated and thenaligned with and mounted onto the pixel layer. In one example, theoptical filter is fabricated by coating a fused silica substrate.Photoactive optical polymer is then deposited over the optical filter, alens mold defining an array of lens forms placed over the photoactiveoptical polymer, and a UV light source activated to cure the photoactiveoptical polymer into a pattern of lenses across the optical filter.Standoffs are similarly molded or formed across the optical filter viaphotolithography techniques. The aperture layer is separately fabricatedby selectively metallizing a glass wafer and etching apertures into thismetallic layer; the glass wafer is then bonded or otherwise mounted tothese standoffs. In this example, the assembly is subsequently inverted,and a second set of standoffs is similarly fabricated across the opticalfilter opposite the lens layer. The pixel layer (e.g., a discrete imagesensor) is aligned with and bonded to the second set of standoffs; thebulk receiving optic is similarly mounted over the aperture layer tocomplete the sensing circuit stack.

Alternatively, the bulk receiving optic, the aperture layer, the lenslayer, and the optical filter, can be fabricated directly onto anun-diced semiconductor wafer—containing the sense pixel—viaphotolithography and wafer-level bonding techniques. However, the bulkreceiving optic, the aperture layer, the lens layer, the optical filter,and the pixel layer can be fabricated and assembled in any other way andwith any other method or technique.

4. Output Circuit

As shown in FIG. 1, the system 100 includes an output circuit, includinga bulk transmitting optic and an illumination source. In oneimplementation, the bulk transmitting optic: is substantially identicalto the bulk receiving optic in material, geometry (e.g., focal length),thermal isolation, etc.; and is adjacent and offset laterally and/orvertically from the bulk receiving optic. In the implementation, theillumination source includes a monolithic VCSEL array of opticalemitters arranged behind the bulk transmitting optic. In one example,the illumination source can include a bar diode laser defining a columnof optical emitters characterized by an emitter pitch distancesubstantially identical to the sense aperture pitch distance; becausethe bar diode laser includes optical emitters fabricated on the samechip, the optical emitters can exhibit substantially similar outputwavelength characteristics as a function of temperature. In thisexample, each optical emitter can output an illuminating beam of aninitial diameter substantially identical to (or slightly greater than)the diameter of a corresponding sense aperture in the aperture layer,and the illumination source can be arranged along the focal plane of thebulk transmitting optic such that each illuminating beam projected fromthe bulk transmitting optic into the field intersects and is ofsubstantially the same size and geometry as the field of view of thecorresponding sensing circuit at any distance from a system 400 (e.g., avariation of the system 100), as shown in FIG. 4. Therefore, theillumination source and the bulk transmitting optic can cooperate toproject substantially all output power into the fields of view of thesensing circuits with relatively minimal power wasted illuminatingsurfaces in space outside of the fields of view of the sensing circuits.

5. Calibration Circuit

As shown in FIG. 1, the system 100 further includes a calibrationcircuit, including an optical bypass 105, a calibration aperture 125defined in the aperture layer 104, a calibration lens 108 incorporatedinto the lens layer 106, an optical filter 109 shared with the sensingcircuit (e.g., sense aperture 120, sense lens 107, sense pixel 111), anda calibration pixel 112 incorporated into the pixel layer 110.Generally, the optical bypass 105 functions to funnel some light raysoutput by the illumination source 103 to the calibration aperture 125;like the sense aperture 120, sense lens 107, and optical filter 109 inthe sensing circuit, the calibration aperture 125, calibration lens 108,and optical filter 109 in the calibration circuit pass a substantiallynarrow wavelength band of light received from the optical bypass to thecalibration pixel. Based on the number of incident photons, frequency ofincident photons, or incident light power, etc. detected by thecalibration pixel within a sampling period, the system 100 can determinewhether and/or to what extent the center (or primary) output wavelengthof the illumination source 103 is matched to an effective center (orprimary) operating wavelength of the calibration circuit 130, and thesystem 100 can modify an output of the temperature regulator accordinglyto shift the output wavelength of the illumination source to theeffective operating wavelength of the calibration circuit 130.

Because the calibration aperture 125, the calibration lens 108, and thecalibration pixel 112 are integrated into the same aperture layer 104,lens layer 106, and pixel layer 110 as the sense aperture 120, the senselens 107, and the sense pixel 111 and because the calibration circuit130 and the sensing circuit (e.g., sense aperture 120, sense lens 107,sense pixel 111) share the same optical filter 109, the calibrationcircuit 130 can share substantially identical manufacturing defects(e.g., alignment defects) and can therefore exhibit substantiallyidentical effective operating wavelengths. Furthermore, because theoptical bypass passes some light from the same illumination source thatilluminates the field of view of the sense channel, manipulation of thetemperature regulator to match the output wavelength of the illuminationsource to the effective operating wavelength of the calibration circuitalso matches the output wavelength of the illumination source to theeffective operating wavelength of the sensing circuit, therebyincreasing the power efficiency of the system 100.

Therefore: the calibration aperture can be formed into the aperturelayer at substantially the same time and with substantially the samepositional accuracy as the sense aperture; the calibration lens can beformed into the lens layer at substantially the same time and withsubstantially the same positional accuracy as the sense lens; and thecalibration pixel can be incorporated into the pixel layer atsubstantially the same time and with substantially the same positionalaccuracy as the sense pixel, such as according to the methods andtechniques described above. The optical filter can also define asingular or unitary structure that spans the calibration circuit and thesensing circuit, and the aperture layer, the lens layer, the opticalfilter, and the pixel layer —including both the calibration and sensingcircuits —can be assembled as described above.

In one implementation, the bulk transmitting optic is arranged in planewith and laterally offset from the bulk receiving optic, and the opticalbypass “siphons” light from one end of the illumination source behindthe bulk transmitting optic to an adjacent region behind the bulkreceiving optic and into the calibration aperture, as shown in FIGS. 1and 4. For example, in the implementation described above in which theillumination source includes a bar diode laser with multiple opticalemitters, the optical bypass can include a light pipe or an opticalwaveguide that extends from one end emitter on the bar diode laser andterminates over the calibration aperture behind the bulk receivingoptic. However, the optical bypass can include any other structure andcan function in any other way to communicate light from the illuminationsource into the calibration circuit.

6. Calibration

In the embodiment of FIG. 2A, the system 200 further includes atemperature regulator 213 coupled to the illumination source andconfigured to modify a temperature of the illumination source based on alight power detected by the calibration pixel. Generally, at startupand/or during operation, the system 200 can read a number of incidentphotons, a frequency of incident photons, or an incident light power,etc. detected by the calibration pixel within a sampling period and canimplement closed-loop feedback control techniques to modify the outputof the temperature regulator—and therefore the temperature and thecenter (or primary) output wavelength of the illumination source—basedon the output of the calibration pixel.

In one implementation, the system 200 further includes a temperaturesensor 230 thermally coupled to the illumination source. In thisimplementation, upon startup, the system 200: ramps up the duty cycle(e.g., the heat output) of the temperature regulator and implementsclosed-loop feedback controls to hold the illumination source at a lowoperating temperature (e.g., 80° C.); and stores an incident photoncount (or frequency of incident photons, etc.) recorded by thecalibration pixel over a sampling period while the illumination sourceis held at the low operating temperature. The system 200 then steps upthe duty cycle of the temperature regulator to achieve discretetemperature steps (e.g., 0.5° C. steps) from the low operatingtemperature to a high operating temperature (e.g., 85° C.) at theillumination source; and stores an incident photon count recorded by thecalibration pixel over a sampling period each temperature step withinthe operating temperature range. (The system 200 can also read incidentphoton counts from the calibration pixel over multiple sampling periodsper temperature step and record a median or average photon count for thetemperature step.) In this implementation, the system 200 can thenidentify a peak incident photon count read from the calibration pixelacross the set of temperature steps, set a corresponding temperature ofthe illumination source as an initial target operating temperature, andadjust the duty cycle of the temperature regulator to achieve theinitial target operating temperature.

In the foregoing implementation, throughout continued operation, thesystem can: read incident photon counts from the calibration pixel;detect variations in the incident photon count read by the calibrationpixel, such as beyond a threshold variance (e.g., 5%); and modify theoutput of the temperature regulator accordingly. The system can also:read the temperature of the illumination source from the temperaturesensor at corresponding sampling periods; and determine whether toincrease or decrease the duty cycle of the temperature regulatorresponsive to changes in the incident photon count on the calibrationpixel based on changes in the temperature of the illumination optic. Forexample, if the incident photon count recorded by the calibration pixeldrops across two or more sampling periods and the temperature sensorindicates that the temperature of the illumination source has alsodropped, the system can increase the heat output of the temperatureregulator and store temperatures of the illumination source as theincident photon count recorded by the configuration pixel increases. Asthe incident photon count reaches a peak value and then begins todecrease with increasing temperature of the illumination source, thesystem can identify a new target operating temperature of theillumination source corresponding to a peak incident photon countrecorded by the calibration pixel during the temperature ramp and thenreduce the output of the temperature regulator to achieve this newtarget operating temperature.

In another example, if the incident photon count recorded by thecalibration pixel drops over two or more sampling periods and thetemperature sensor indicates that the temperature of the illuminationsource increased over the same sampling periods, the system can reducethe heat output of the temperature regulator and store temperatures ofthe illumination source as the incident photon count recorded by thecalibration pixel increases. As the recorded incident photon countreaches a peak value and then begins to decrease with decreasingtemperature of the illumination source, the system can identify a newtarget operating temperature corresponding to a peak incident photoncount recorded by the calibration pixel during the temperature drop andincrease the output of the temperature regulator to achieve this newtarget operating temperature.

In yet another example, if the incident photon count recorded by thecalibration pixel drops beyond the threshold variation over two or moresampling periods but no substantial temperature change is detected atthe illumination source over the sampling periods, the system can rampup the heat output of the temperature regulator to achieve a one-stepincrease in temperature of the illumination source. If the incidentphoton count recorded by the calibration pixel increases in response tothe increase in temperature of the illumination source, the system can:continue to increase the output of the temperature regulator until theincident photon begins to drop, determine a new (higher) targetoperating temperature corresponding to the new peak incident photoncount recorded by the calibration pixel during this temperature ramp;and reduce the output of the temperature regulator to achieve this newtarget operating temperature, as in the foregoing example. However, ifthe incident photon count recorded by the calibration pixel decreases inresponse to the increase in temperature of the illumination source, thesystem can step down the heat output of the temperature regulator. Asthe incident photon count increases and then begins to decrease with thedecrease in temperature of the illumination source, the system can:determine a new (lower) target operating temperature corresponding to apeak incident photon count recorded by the calibration pixel during thistemperature drop; and increase the output of the temperature regulatorto achieve this new target operating temperature, as in the foregoingexample.

The system can therefore implement closed-loop feedback techniques toachieve an output of the temperature regulator that maintains theillumination source at a temperature corresponding to a center (orprimary) output wavelength of the illumination source substantiallymatched to the effective operating wavelength of the sensing circuitbased on a number of photons (or a frequency of photons, a time betweenconsecutive photons, etc.) detected by the single calibration pixel.

In other implementations, the system can vary the output wavelength ofthe illumination source by: actively tuning an internal Fabrey-Perotcavity thickness in a laser, such as via a MEMS actuator orpiezoelectric film within the cavity; actively tuning an external cavitylength of a vertical external-cavity surface-emitting laser (“VECSEL”),such as with MEMS actuators. In still other implementations, the systemcan vary the transmit wavelength (e.g., passband center wavelength) ofthe receiver circuit by: actively tuning a center wavelength of a filterwithin the receiver circuit by angle tuning, such as by rotating thefilter with a MEMS gimbal actuator; etc. Of course, in some embodiments,the system can vary the output wavelength of the illumination source asdiscussed above in addition to varying the transmit wavelength of thereceiver circuit. In the foregoing implementations, the system canimplement closed-loop methods and techniques to actively and dynamicallytune the output wavelength of the illumination source and/or thereceiver circuit, as described herein.

7. Extended One-Dimensional Calibration Circuit

One variation of the system is illustrated in FIGS. 3A AND 3B as system300. In this embodiment, system 300 includes a set of (e.g., four)calibration circuits per illumination optic, such as 330-0, 330-1,330-2, 330-3. In this variation: calibration apertures (e.g., 325-0,325-1, etc.) in the set of calibration circuits can be formed into theaperture layer at substantially the same time and with substantially thesame positional accuracy as the sense aperture; calibration lenses inthe set of calibration circuits can be formed into the lens layer atsubstantially the same time and with substantially the same positionalaccuracy as the sense lens; and calibration pixels in the set ofcalibration circuits can be incorporated into the pixel layer atsubstantially the same time and with substantially the same positionalaccuracy as the sense pixel, such as according to the methods andtechniques described above. The optical filter can also define asingular or unitary structure that spans the set of calibration circuitsand the sensing circuit, and the aperture layer, the lens layer, theoptical filter, and the pixel layer —including both the calibration andsensing circuits —can be assembled as described above. Furthermore, inthis variation, the optical bypass can siphon light from theillumination source into each calibration aperture in the set ofcalibration circuits, as shown in FIGS. 3A and 3B.

In this variation, calibration lenses can be positioned in the lenslayer such that, when the aperture layer is assembled over the lenslayer, select calibration aperture and calibration lens pairs arelaterally and/or longitudinally offset. Because a particular calibrationlens in the set of calibration circuits is thus deliberately offset fromits paired calibration aperture in the assembly, the particularcalibration lens can pass light—received from the aperture —toward theoptical filter at a corresponding off-axis angle. In one example of anominal assembly (i.e., an assembly in which a first calibrationaperture and first calibration lens are axially aligned) including fourcalibration circuits: the first calibration lens can be axially alignedwith the first aperture to output light toward the optical filter at anangle of 0° from normal to the optical filter; a second calibration lenscan be laterally offset from a second aperture by a first distance inorder to output light toward the optical filter at an angle of 1° fromnormal to the optical filter; a third calibration lens can be laterallyoffset from a third aperture by a second distance greater than the firstdistance in order to output light toward the optical filter at an angleof 2° from normal to the optical filter; and a fourth calibration lenscan be laterally offset from a fourth aperture by a third distancegreater than the second distance in order to output light toward theoptical filter at an angle of 3° from normal to the optical filter, asshown in FIGS. 2A and 2C.

In this variation, the system can execute a method for calibrating anoptical distance sensor, including: calculating a first photon count ofphotons detected by a first calibration pixel axially aligned with afirst calibration lens axially aligned with a first calibrationaperture; calculating a second photon count of photons detected by asecond calibration pixel axially offset from a second calibration lensaxially offset from a second calibration aperture by a first offsetdistance; transforming the first photon count and the second photoncount into a target temperature change at an illumination source; andactuating a temperature regulator coupled to the illumination sourceaccording to the target temperature change.

In particular, during operation, the system can read incident photoncounts (or times between consecutive incident photons, etc.) from eachcalibration pixel, characterize a difference between the effectiveoperating wavelength of the calibration circuit and the center (orprimary) output wavelength of the illumination source during a samplingperiod based on a pattern of incident photon counts read from thecalibration pixels, and then maintain, increase, or decrease the outputof the temperature regulator accordingly, as shown in FIG. 2C. In oneimplementation, if the first calibration circuit records an incidentphoton count greater than incident photon counts recorded by the othercalibration circuits in the system, the system can determine that thecenter output wavelength of the illumination source is either matched toor is greater than the effective operating wavelength of the firstcalibration circuit. The system can then determine that the outputwavelength of the illumination source is too low if the incident photoncount (or the incident photon frequency, etc.) recorded by the firstcalibration pixel is less than a present threshold value, if theincident photon count recorded by the fourth calibration pixel is lessthan a present threshold value, or if a difference or ratio between theincident photon counts read by the first and second calibration pixelsis less than a preset threshold value, etc. and decrease the heat outputof the temperature regulator accordingly, thereby decreasing the outputwavelength of the illumination source. However, in this implementation,if the second calibration circuit records an incident photon countgreater than the incident photon counts recorded by the othercalibration circuits in the system, including the first calibrationcircuit, the system can determine that the center output wavelength ofthe illumination source is less than the effective operating wavelengthof the first calibration circuit and increase the heat output of thetemperature regulator at a first rate accordingly, thereby increasingthe output wavelength of the illumination source. Furthermore, in thisimplementation, if the third calibration circuit records an incidentphoton count greater than the incident photon counts recorded by theother calibration circuits in the system, including the first and secondcalibration circuits, the system can determine that the center outputwavelength of the illumination source is again less than the effectiveoperating wavelength of the first calibration circuit and increase theheat output of the temperature regulator at a second rate greater thanthe first rate accordingly, thereby more rapidly increasing the outputwavelength of the illumination source. The system can therefore activelyadjust the output of the temperature regulator substantially inreal-time based on incident photon counts recorded by the calibrationpixels throughout operation.

Alternatively, the system can locally store a set of photon counttemplates (or lookup tables, etc.), wherein each photon count templateincludes absolute or relative incident photon count values for the setof calibration circuits at a particular absolute or relative differencebetween the effective operating wavelength of the sensing circuit andthe center (or primary) output wavelength of the illumination source.The system can thus implement template matching techniques to match aset of incident photon counts recorded by the set of calibration pixelsduring a sampling period to a particular photon count template in theset of photon count templates and then modify the heat output of theillumination source accordingly, such as based on a heat output changetarget associated with the matched photon count template. However, thesystem can implement any other method or technique to transform incidentphoton counts read by the set of calibration circuits during a samplingperiod into a new heat output target for the illumination source. Thesystem can repeat this process for each sampling period (or each set ofconsecutive sampling periods) throughout operation to maintain alignmentbetween the center output wavelength of the illumination source andeffective operating wavelength of the sensing circuit.

8. Defect Compensation in Extended Calibration Circuit

In another example of the system that includes four calibration circuitsrealizing different light output angles at the optical filter, the lenslayer can be misaligned with the aperture layer due to manufacturingdefects or manufacturing limitations such that: the first calibrationlens is offset from the first aperture by a first distance and thusoutputs light toward the optical filter at an angle of −1° from normalto the optical filter; the second calibration lens is substantiallyaxially aligned with the second aperture and thus outputs light towardthe optical filter at an angle of 0° from normal to the optical filter;the third calibration lens is laterally offset from the third apertureby the first distance and thus outputs light toward the optical filterat an angle of 1° from normal to the optical filter; and the fourthcalibration lens is laterally offset from the fourth aperture by asecond distance greater than the first distance and thus outputs lighttoward the optical filter at an angle of 2° from normal to the opticalfilter, as shown in FIG. 2D. In this example, the system can implementmethods and techniques described above to adjust the heat output of theillumination source in order to substantially maximize the incidentphoton count (or incident photon frequency, etc.) recorded by the firstcalibration pixel per unit time. As described above, if the first andthird calibration circuits record substantially similar incident photoncounts that are also greater than incident photon counts recorded by thesecond and fourth calibration circuits, the system can determine thatthe center output wavelength of the illumination source is eithermatched to or is greater than the effective operating wavelength of thefirst calibration circuit, as shown in FIG. 2D. The system can thendetermine that the output wavelength of the illumination source is toolow if the incident photon count (or the incident photon frequency,etc.) recorded by the first calibration pixel is less than a presentthreshold value or if a difference (or if a ratio between incidentphoton counts read by the first and second calibration pixels is lessthan a preset threshold value, etc.) and decrease the heat output of thetemperature regulator accordingly, thereby decreasing the outputwavelength of the illumination source. However, in this implementation,if the fourth calibration circuit records an incident photon countgreater than the incident photon counts recorded by the othercalibration circuits in the system, the system can determine that thecenter output wavelength of the illumination source is less than theeffective operating wavelength of the first calibration circuit and canincrease the heat output of the temperature regulator accordingly, asshown in FIG. 2D, thereby increasing the output wavelength of theillumination source. Alternatively, the system can implement templatematching techniques to match incident photon counts recorded by the setof calibration pixels during a sampling period to a photon counttemplate and modify the heat output of the temperature regulatoraccordingly, as described above.

In a similar example in which the lens layer is misaligned with theaperture layer: the first calibration lens is offset from the firstaperture by a first distance and thus outputs light toward the opticalfilter at an angle of −0.5° from normal to the optical filter; thesecond calibration lens is offset from the second aperture by the firstdistance and thus outputs light toward the optical filter at an angle of0.5° from normal to the optical filter; the third calibration lens islaterally offset from the third aperture by a second distance greaterthan the first distance and thus outputs light toward the optical filterat an angle of 1.5° from normal to the optical filter; and the fourthcalibration lens is laterally offset from the fourth aperture by a thirddistance greater than the second distance and thus outputs light towardthe optical filter at an angle of 2.5° from normal to the opticalfilter.

In another example, the system performs an initial calibration by:scanning the illumination source across a range of output wavelengths(e.g., by varying the temperature of the illumination source across anoperating range); recording incident photon counts per unit time acrossthe set of calibration pixels in a calibration template for variousoutput wavelengths of the illumination source during the scan (or ateach discrete temperature of the illumination source during the scan);recording incident photon counts per unit time across the sense pixelsfor various output wavelength of the illumination source during thescan; identifying a particular illumination source wavelength (ortemperature) yielding a highest incident photon counts per unit timeacross the sense pixels; and setting a particular calibration template—corresponding to the particular illumination source wavelength —fromthe scan as a target calibration template. Later, during operation, thesystem can vary the output wavelength of the illumination source (e.g.,by varying the temperature of the illumination source) to match incidentphoton counts per unit time across the set of calibration pixels to thetarget calibration template.

However, the calibration apertures and calibration lenses can benominally offset according to any other schema and can be offset in anyother way due to manufacturing defects, manufacturing limitations, etc.The system can also implement any other method or technique tocharacterize alignment between the effective operating wavelength of thecalibration circuit —and therefore the sensing circuit —and theillumination source and to modify the heat output of the temperatureregulator accordingly.

9. Extended Two-Dimensional Calibration Circuit

In another implementation, the system includes calibration circuitsarranged along multiple axes. For example, the system can include: afirst calibration circuit arranged at an origin position and configuredto pass light toward the optical filter at an angle of 0° in a nominalsystem assembly; a second calibration circuit laterally offset (e.g.,offset along an X-axis) from the first calibration circuit andconfigured to pass light toward the optical filter at an angle of 1° inthe nominal system assembly; a third calibration circuit laterallyoffset from the second calibration circuit and configured to pass lighttoward the optical filter at an angle of 2° in the nominal systemassembly; a fourth calibration circuit longitudinally offset (e.g.,offset along a Y-axis) from the first calibration circuit and configuredto pass light toward the optical filter at an angle of 1° in the nominalsystem assembly; and a fifth calibration circuit longitudinally offsetfrom the third calibration circuit and configured to pass light towardthe optical filter at an angle of 2° in the nominal system assembly.This two-dimensional array of calibration circuits can thus collectincident photon data symptomatic of both a lateral offset andlongitudinal offset of the lens layer relative to the aperture layer,and the system can modify the heat output of the temperature regulatorbased on absolute or relative differences between incident photon countsrecorded across the five calibration pixels, such as according tomethods and techniques described above, in order to align the centeroutput wavelength of the illumination source to the effective operatingwavelength of the sensing circuit, thereby compensating for both thelateral offset and the longitudinal offset of the lens layer relative tothe aperture layer.

10. Multiple Illumination Sources

In one variation, the system further includes multiple discreteillumination sources. In this variation, each illumination source ispaired with: one discrete bulk transmitting optic; a calibration circuit(or set of calibration circuits) integrated into the aperture layer,lens layer, the optical filter, and the pixel layer; and an opticalbypass interposed between the illumination source and the calibrationaperture(s) of the corresponding calibration circuit(s). For example,the system can include: a first bulk transmitting optic and a secondbulk transmitting optic on opposing longitudinal sides of the bulkreceiving optic; a first illumination optic behind the first bulktransmitting optic; and a second illumination optic behind the secondbulk transmitting optic. In this example, each illumination source andits corresponding bulk transmitting optic can project a set ofilluminating beams into the fields of view of corresponding sensingcircuits in the system, thereby achieving twice the illumination powerper field of view of the sensing circuits compared to a system with asingle like illumination source.

However, in this variation, various illumination sources in the systemmay exhibit differences in their outputs during operation, such asdifferent center output wavelengths for a particular operatingtemperature and/or different changes in center output wavelength perchange in operating temperature. The system can therefore include adiscrete optical bypass and calibration circuit(s) per illuminationsource. In particular, in the foregoing example, the system can includea first optical bypass extending from the first illumination source to afirst calibration aperture over a first longitudinal side of theaperture layer; a second optical bypass extending from the secondillumination source to a second calibration aperture over a secondlongitudinal side of the aperture layer opposite the first side of theaperture layer; a first temperature regulator thermally coupled to thefirst illumination source; and a second temperature regulator thermallycoupled to the second illumination source and controlled independentlyof the first temperature regulator. The system can thus implement theforegoing methods and techniques to match the center output wavelengthof the first illumination source to the effective operating wavelengthof its corresponding calibration circuit independently of the secondillumination source; and vice versa.

However, in this variation, the system can include any other number andconfiguration of illumination sources, bulk transmitting optics, opticalbypasses, temperature regulators, and calibration circuits in order toilluminate fields of view defined by the sensing circuits and to matchthe output wavelength of each illumination source to the effectiveoperating wavelength of the sensing circuits.

The systems and methods described herein can be embodied and/orimplemented at least in part as a machine configured to receive acomputer-readable medium storing computer-readable instructions. Theinstructions can be executed by computer-executable componentsintegrated with the application, applet, host, server, network, website,communication service, communication interface,hardware/firmware/software elements of a user computer or mobile device,wristband, smartphone, or any suitable combination thereof. Othersystems and methods of the embodiment can be embodied and/or implementedat least in part as a machine configured to receive a computer-readablemedium storing computer-readable instructions. The instructions can beexecuted by computer-executable components integrated bycomputer-executable components integrated with apparatuses and networksof the type described above. The computer-readable medium can be storedon any suitable computer readable media such as RAMs, ROMs, flashmemory, EEPROMs, optical devices (CD or DVD), hard drives, floppydrives, or any suitable device. The computer-executable component can bea processor but any suitable dedicated hardware device can(alternatively or additionally) execute the instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the embodiments of the invention without departing fromthe scope of this invention as defined in the following claims.

What is claimed is:
 1. An optical system for performing distancemeasurements, the optical system comprising: an optical imaging receivemodule comprising a bulk receiver optic, an aperture layer including aplurality of apertures, a lens layer including a plurality of lenses anda pixel layer including a plurality of sense pixels, a plurality ofsensor channels and at least one calibration channel, wherein eachsensor channel in the plurality of sensor channels and the at least onecalibration channel includes an aperture from the plurality ofapertures, a lens from the plurality of lenses and a sense pixel fromthe plurality of sense pixels; and an optical imaging transmit modulecomprising a bulk transmitter optic and an illumination sourcecomprising a plurality of optical emitters configured to output light atan operating wavelength as a function of a parameter, project a firstportion of the light into a field ahead of the optical system andproject a second portion of the light onto the sense pixel in thecalibration channel; and a regulator configured to modify the parameterof the plurality of optical emitters based on a light power detected bythe sense pixel in the calibration channel.
 2. The optical system forperforming distance measurements set forth in claim 1 wherein eachsensor channel in the plurality of sensor channels defines a discretefield of view in a field ahead of the optical imaging receive module. 3.The optical system for performing distance measurements set forth inclaim 2 wherein each discrete field of view is non-overlapping beyond athreshold distance from the optical system.
 4. The optical system forperforming distance measurements set forth in claim 1 further comprisingan optical filter disposed between the plurality of lenses and theplurality of sense pixels, the optical filter configured to receivelight from the plurality of lenses and pass light to the plurality ofsense pixels at a narrow band of wavelengths that includes the operatingwavelength while blocking light outside the narrow band.
 5. The opticalsystem for performing distance measurements set forth in claim 1 whereinthe regulator is configured to modify a temperature of each emitter inthe plurality of optical emitters.
 6. The optical system for performingdistance measurements set forth in claim 5 wherein each sense pixel inthe plurality of sense pixels comprises an array of single-photonavalanche detectors (SPADs) and each optical emitter in the plurality ofoptical emitters comprises a vertical-cavity surface-emitting laser(VCSEL).
 7. The optical system for performing distance measurements setforth in claim 6 wherein the regulator is configured to actively tune anexternal cavity length of the VCSELs.
 8. The optical system forperforming distance measurements set forth in claim 1 wherein theplurality of optical emitters includes a first set of optical emittersconfigured to project a plurality of discrete illuminating beams throughthe bulk transmitter optic and a second optical emitter configured toproject a discrete illuminating beam onto the sense pixel in thecalibration channel, wherein each of the optical emitters in the firstset of optical emitters and the second optical emitter exhibitsubstantially similar output wavelength characteristics as a function oftemperature.
 9. The optical system for performing distance measurementsset forth in claim 8 further comprising an optical bypass extending fromthe second optical emitter to the at least one calibration channel, theoptical bypass configured to direct the discrete illuminating beamprojected by the second optical emitter to the calibration channel. 10.An optical system for performing distance measurements, the opticalsystem comprising: an optical imaging receive module comprising a bulkreceiver optic configured to project incident light rays from outsidethe system toward a focal plane within the optical imaging receivemodule, an aperture layer coincident with the focal plane and includinga plurality of apertures extending through the aperture layer surroundedby a stop region, a lens layer including a plurality of lenses, a pixellayer including a plurality of sense pixels, an optical filter disposedbetween the plurality of lenses and the plurality of sense pixels, aplurality of sensor channels and at least one calibration channel,wherein each sensor channel in the plurality of sensor channels and theat least one calibration channel includes an aperture from the pluralityof apertures, a lens from the plurality of lenses and a sense pixel fromthe plurality of sense pixels, and wherein each sensor channel in theplurality of sensor channels defines a discrete field of view in a fieldahead of the optical imaging receive module that is non-overlappingbeyond a threshold distance from the optical system and wherein eachsensor channel in the plurality of sensor channels is configured tocommunicate light incident from the bulk receiver optic to the sensepixel of the sensor channel through the lens of the sensor channel andthrough the optical filter; and an optical imaging transmit modulecomprising a bulk transmitter optic and an illumination sourcecomprising a plurality of optical emitters configured to output light atan operating wavelength as a function of a parameter, project a firstportion of the light into a field ahead of the system and project asecond portion of the light onto the sense pixel in the calibrationchannel; and a temperature regulator configured to modify a temperatureof the light output by the plurality of optical emitters based on alight power detected by the sense pixel in the calibration channel. 11.The optical system for performing distance measurements set forth inclaim 10 wherein each sense pixel in the plurality of sense pixelscomprises an array of single-photon avalanche detectors (SPADs), eachoptical emitter in the plurality of optical emitters comprises avertical-cavity surface-emitting laser (VCSEL), and the temperatureregulator is configured to actively tune an external cavity length ofthe VCSELs.
 12. The optical system for performing distance measurementsset forth in claim 11 wherein stop region of the aperture layer rejectsincident light rays and, for each sensor channel, the aperture of thechannel passes incident light rays towards the sense pixel of thechannel through the optical filter, and wherein the optical filter isconfigured to pass light to the sense pixel at a narrow band ofwavelengths that includes the operating wavelength while blocking lightoutside the narrow band.
 13. The optical system for performing distancemeasurements set forth in claim 12 wherein the optical system can scan avolume to collect three-dimensional distance data that can bereconstructed into a virtual three-dimensional representation of thevolume.
 14. An optical system for performing distance measurements, theoptical system comprising: an optical imaging receive module comprisinga bulk receiver optic, an aperture layer coincident with the focal planeand including a plurality of apertures extending through the aperturelayer surrounded by a stop region, a lens layer including a plurality oflenses and a pixel layer including a plurality of sense pixels, aplurality of sensor channels and at least one calibration channel,wherein each sensor channel in the plurality of sensor channels and theat least one calibration channel includes an aperture from the pluralityof apertures, a lens from the plurality of lenses and a sense pixel fromthe plurality of sense pixels; and an optical imaging transmit modulecomprising a bulk transmitter optic and an illumination sourcecomprising a plurality of optical emitters configured to output a bandof wavelengths as a function of a parameter, the plurality of opticalemitters including a first set of optical emitters configured to projecta discrete illuminating beam through the bulk transmitter optic and asecond optical emitter, wherein each of the optical emitters in thefirst set of optical emitters and the second optical emitter exhibitsubstantially similar output wavelength characteristics as a function oftemperature; an optical bypass extending from the second optical emitterto the at least one calibration channel, the optical bypass configuredto direct a discrete beam projected by the second optical emitter to thecalibration channel; and a regulator configured to modify the parameterof the plurality of optical emitters based on a light power detected bythe sense pixel in the calibration channel.
 15. The optical system forperforming distance measurements set forth in claim 14 wherein eachsensor channel in the plurality of sensor channels defines a discretefield of view in a field ahead of the optical imaging receive module.16. The optical system for performing distance measurements set forth inclaim 15 wherein each discrete field of view is non-overlapping beyond athreshold distance from the optical system.
 17. The optical system forperforming distance measurements set forth in claim 14 furthercomprising an optical filter disposed between the plurality of lensesand the plurality of sense pixels, the optical filter configured toreceive light from the plurality of lenses and pass light at anoperating wavelength to the plurality of sense pixels.
 18. The opticalsystem for performing distance measurements set forth in claim 14wherein the regulator is configured to modify a temperature of eachemitter in the plurality of emitters.
 19. The optical system forperforming distance measurements set forth in claim 18 wherein eachsense pixel in the plurality of sense pixels comprises an array ofsingle-photon avalanche detectors (SPADs) and each optical emitter inthe plurality of optical emitters comprises a vertical-cavitysurface-emitting laser (VCSEL).
 20. The optical system for performingdistance measurements set forth in claim 19 wherein the regulator isconfigured to actively tune an external cavity length of the VCSELs.